PROJECT SUMMARY ? Project 2 Smoking cessation in young adulthood is critical to preventing tobacco-related disease and death, particularly among socioeconomically-disadvantaged young adults (SDYAs) who are at greatest risk of tobacco-related health disparities. There are few efficacious smoking cessation interventions targeted to young adult (YA) smokers and while recent studies highlight that mobile and social media approaches to smoking cessation are acceptable to YA smokers, existing approaches are less effective in SDYA smokers. The overarching aim of the current study is to delineate how best to frame and deliver an efficacious smoking cessation intervention for SDYA smokers to improve cessation outcomes in this at-risk group. First, we will conduct formative research informed by behavioral economic theory on biases in decision-making to identify barriers to cessation, potential targets for cessation messages, and preferred mobile and social media modalities for smoking cessation intervention (e.g., text message, social media post, social media challenge) in SDYA smokers. Findings from this work will inform the development of themes/messages related to key drivers of smoking and barriers to cessation in SDYAs. Through iterative message testing, we will develop a library of cessation-related themes and messages for SDYAs that reflect the highest levels of personal relevance, likeability, and perceived effectiveness of messages. Our formative work will also inform a content delivery strategy (i.e., frequency of messaging, delivery of particular messages via text or social media, use of video and other creative content). Second, we will conduct a randomized controlled smoking cessation trial to test the efficacy of a tailored intervention for SDYA smokers using our curated content library and content delivery strategy. This work will concurrently build the evidence base on the distinct needs and challenges faced by SDYA smokers, while developing and testing smoking cessation intervention content uniquely relevant to this group. This study is aligned with two of the National Cancer Institute's tobacco control research priorities: 1) it addresses how tobacco interventions can be tailored or re-engineered to improve smoking-cessation outcomes in a group at particular risk for tobacco-related health disparities; and 2) it tests a novel intervention strategy to reduce young adult tobacco use that could be extended to other areas of cancer prevention in a low-cost, scalable format.